The invention pertains to a semiconductor image sensing device. More particularly, the invention pertains to a semiconductor image sensing device in which defective segments caused by inoperative lines of photosensing elements are eliminated from the video output signal produced by the device.
With reference now to FIG. 1, a prior art image sensing device of the same general type to which the invention pertains is illustrated. The device includes a pixel (picture element) array 12 composed of a number of lines and columns of pixels 13. Each pixel 13 may be represented schematically as a photosensitive diode and an FET transistor. The gate electrodes of the FET transistors of the pixels 13 are connected in rows to corresponding ones of vertical lines 14, while the drain electrodes of the FETs are connected in columns to respective horizontal lines 15. (Although in the drawing the vertical lines 14 and the horizontal lines 15 extend in the horizontal and vertical directions, respectively, they are properly termed vertical and horizontal lines since the vertical lines 14 are scanned in the vertical direction and the horizontal lines 15 are scanned in the horizontal direction.) Each of the vertical lines 14 is connected to a corresponding output line from a vertical shift register 11. If desired, an interlace circuit can be provided between the vertical shift register 11 and the array 12 to effect interlaced scanning if the array is used in a television camera.
The horizontal lines 15 are connected to source electrodes of respective output switch FETs 16. The drain electrodes of the FETs 16 are connected in common to the input terminal of an amplifier 18, and the gate electrodes of the FETs 16 are coupled to corresponding outputs of a horizontal shift register 17. The output of the amplifier 18 is applied to the input of a fixed-pattern noise suppressing circuit 19. The output signal from the device is formed at the output of the noise suppressing circuit 19.
In operation, starting from a reset state, when the pixel array 12 is exposed to an image to be sensed, the diode portions of the pixels 13 conduct in an amount determined by the intensity of the light in respective portions of the image. Accordingly, the capacitance associated with each of the pixels 13 is discharged in an amount determined by the intensity of the light in the corresponding portion of the image being sensed. After the pixel array 12 has been exposed to light, the vertical shift register 11 is activated by a clock signal .phi..sub.V to shift a pulse through the shift register one position at a time. Accordingly, the vertical lines 14 receive an activating signal in sequence. Activation of each of the vertical lines 14 in this manner causes the FETs of the associated row of pixels 13 to be turned on, thus transferring the charge from the capacitance of each pixel 13 to the corresponding one of the horizontal lines 15.
The horizontal shift register 17 is then activated to shift a pulse therethrough, one position for each pulse of a horizontal clocking signal .phi..sub.V, thereby turning on the output switch FETs 16 one at a time and connecting the horizontal lines 15 one at a time to the input of the amplifier 18. The horizontal shift register 17 makes one complete cycle for activation for each of the vertical lines 14. The amplifier 18 boosts the voltage on its input terminal produced by the sequential transfer thereto of the charge packets from the various pixels 13 to thereby produce a video signal. Fixed-pattern noise is suppressed by the fixed-pattern noise suppressing circuit 19 in a known manner.
The prior art arrangement illustrated in FIG. 1 would perform quite well in the case that the entire pixel array 12 contains no defects. However, in the case, for example, that one of the horizontal lines 15 is short circuited to ground so that no output signal can be generated during the read-out period for that line, a vertical streak will appear in the reproduced image at a position corresponding to the position of the defective horizontal line. With no provision being made to conceal such defects, the pixel array would have to be rejected.
Accordingly, it is an object of the present invention to provide a method for concealing defects in a video output signal produced by an image-sensing array.
Further, it is an object of the present invention to provide an image sensing device in which defects in an image-sensing array are effectively concealed.